Control laws for an active tunable vibration absorber designed for rotor blade damping augmentation

Most Individual Blade Control (IBC) approaches have attempted to suppress the rotor vibration by actively altering the varying aerodynamic loads on the blade using techniques such as trailing-edge servo-flaps or imbedded piezoelectric fibres to twist the blade. Unfortunately, successful implementation of these approaches has been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an unique approach that is designed to suppress the rotor vibration by actively altering the structural stiffness of the blade out of phase with the time varying aerodynamic forces. The Smart Spring system is able to adaptively alter the stiffness properties of the blade while requiring only small deformations of the actuator, which overcomes the major problems inherent in the former approaches. The theoretical characterisation of the Smart Spring system as a class of active Tunable Vibration Absorbers (TVA) is presented in the paper. A real-time adaptive control system was developed for a Smart Spring to suppress vibration. Initial aerodynamic wind tunnel test results using the proof-of-concept model of the device in a fixed blade indicate that the Smart Spring can evolve into a powerful approach for IBC.